EESA06H3 Chapter Notes - Chapter 2: Aseismic Creep, Oceanic Trench, Mid-Ocean Ridge
Document Summary
Sometimes the north magnetic poles and south magnetic poles exchange positions. The changes is the polarity of the magnetic field are called magnetic reversals. During the period of normal polarity (such as the present) , magnetic lines of force flow from the south pole to the north pole and are compass needles point to the north. During periods of reversed polarity the lines of magnetic force run the other way and our compass needles would point toward the south. Study of ancient rocks can therefore tell us about the chances of the earth"s magnetic field in the last and this study if ancient magnetic fields recorded in rocks is paleomagnetism. Lava flows contain abundant magnetic minerals and can be isotopically dated. Stacked continental lava flows have been used to construct a magnetic polarity time scale that records the pattern of magnetic reversals over time. Any deviation of magnetic strength from average readings is called anomaly.
